Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations declare readOnlyHint and idempotentHint=false, and the description explains why: every call is charged (x402 USDC or card key), repeats are not free, failed calls are free, and a nonexistent block returns an uncharged 404. That adds billing and error behavior well beyond what the annotations convey, plus an explicit 'changes nothing' safety statement.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose and return fields, then routing, error behavior, example, and pricing. Dense but every sentence carries information; the pricing/credits clause is slightly wordy but is genuinely decision-relevant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description enumerates what the call returns, and it covers error behavior (404), cost implications, and read-only semantics. Nothing an agent needs to call or interpret this correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the single parameter already documents 'latest' as default. The description adds only that a block can be specified by decimal number and repeats the 'latest' example, which is marginal beyond the schema – baseline 3.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource (fetch latest Sei block or any block by decimal number) and enumerates the returned fields (hash, timestamp, tx count, gas used/limit, base fee, producer). It explicitly contrasts with the sibling sei_gas, so an agent can distinguish it without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives positive guidance ('use for timestamps and confirmation counts') and names the alternative for the adjacent need ('for current fees use sei_gas'). The default and example ('number=latest') are also stated, leaving no inference needed.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.